Exhaust purification device burner

ABSTRACT

This burner is disposed at the upstream side of a DPF and raises the temperature of exhaust by combusting an air-fuel mixture of air and fuel in a combustion region within a flame holder. The burner is provided with: an upstream-side cover enclosing the peripheral wall of the flame holder; and a partition wall that partitions the gap between the flame holder and the upstream-side cover into a prior-stage exhaust chamber and a latter-state exhaust chamber. An exhaust tube through which exhaust from an engine flows is connected to the upstream-side cover; a through hole that interconnects the prior-stage exhaust chamber and the latter-stage exhaust chamber is formed at the partition wall; exhaust flows in from the exhaust tube at the prior-stage exhaust chamber; and exhaust flows in from the prior-stage exhaust chamber through the through hole to the latter-stage exhaust chamber.

TECHNICAL FIELD

The technique of the present disclosure relates to a burner for anexhaust purification device. The burner is applied to an exhaustpurification device, which purifies exhaust gas from the engine, andraises the temperature of the exhaust gas.

BACKGROUND ART

Conventional diesel engines include, in the exhaust passage, a dieselparticulate filter (DPF), which captures particulate matter (PM)contained in exhaust gas. In such a DPF, in order to maintain thefunction of capturing particulate matter, a regeneration process, inwhich particulate matter captured by the DPF is burnt, is performed.

For example, Patent Document 1 discloses an exhaust purification device,in which a burner is arranged upstream of a DPF. Exhaust gas with thetemperature raised by the burner is sent to the DPF to regenerate theDPF. In the burner, fuel for the engine and air for combustion areintroduced to a combustion area, which is the inside space of a tubularflame stabilizer, and mixture of the fuel and the air for combustion isproduced. The air-fuel mixture is then burnt by ignition, and thetemperature of the exhaust gas is raised.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    2011-185493

SUMMARY OF THE INVENTION Problem that the Invention is to Solve

While an engine is cold, the temperature of a flame stabilizer and thetemperature of gas in the combustion area are low relative to thoseafter completion of warming-up of the engine. For this reason, when theregeneration process is performed while the engine is cold, unburned gascontained in the combustion gas increases compared to that after thecompletion of the warming-up of the engine.

It is an objective of the technique of the present disclosure to providea burner for an exhaust purification device that reduces fuel dischargedas unburned gas.

Means for Solving the Problems

To achieve the above objective, according to one aspect of the presentdisclosure, a burner for an exhaust purification device (an exhaustpurification device burner) comprises a tubular flame stabilizer havinga space in which air-fuel mixture of fuel and air is combusted and anejection port for ejecting combustion gas, a tubular cover thatsurrounds the flame stabilizer, in which a gap is formed between aninner circumference face of the cover and an outer circumference face ofthe flame stabilizer, an exhaust pipe connected to the cover to deliverexhaust gas into the gap, and a partition portion arranged in the gap topartition the gap into an upstream exhaust chamber and a downstreamexhaust chamber. The upstream exhaust chamber is connected to theexhaust pipe and the downstream exhaust chamber, and the downstreamexhaust chamber is connected to the ejection port of the flamestabilizer.

According to the above aspect, exhaust gas flowing into the gap betweenthe flame stabilizer and the cover takes a more complex route due to thepartition portion. This increases the possibility for the exhaust gas tocontact the flame stabilizer and raises the temperature of the flamestabilizer. Thus, the temperature of gas is more easily raised in thecombustion area heated by the flame stabilizer. As a result, even incold, the temperature of the flame stabilizer and the temperature of thegas in the combustion area are promptly raised, and fuel in thecombustion area is more easily vaporized, so that the fuel discharged asunburned gas after being supplied to the combustion area is reduced.

Preferably, the flame stabilizer is shaped as a cylindrical tube, andthe exhaust pipe extends in the tangential direction of the outercircumferential face of the flame stabilizer.

According to the above aspect, since the exhaust gas flowing into theupstream exhaust chamber more easily swirls around the flame stabilizer,the flows of the exhaust gas are more easily aligned in the upstreamexhaust chamber in one direction. As a result, for example, compared towhen the exhaust gas flowing into the upstream exhaust chamber isdivided into flows in two directions by striking the circumference wallof the flame stabilizer, it is easier for the exhaust gas to contact theportion of the outer circumferential face of the flame stabilizer thatdefines the upstream exhaust chamber. For this reason, heat isefficiently transferred from the exhaust gas to the flame stabilizer.

Preferably, the exhaust pipe connects to an outer circumferential faceof the cover at one location.

According to the above aspect, the exhaust gas is introduced to theupstream exhaust chamber from one location of the upstream exhaustchamber. For this reason, the exhaust gas more easily swirls around theflame stabilizer in the upstream exhaust chamber. As a result, comparedto when an exhaust pipe communicates with the upstream exhaust chamberat a plurality of locations, the flows of the exhaust gas are moreeasily aligned in one direction in the upstream exhaust chamber.

Preferably, the partition portion protrudes from the outercircumferential face of the flame stabilizer toward the innercircumferential face of the cover and is coupled to the outercircumferential face of the flame stabilizer and the innercircumferential face of the cover. The partition portion is a partitionwall that partitions the gap into the upstream exhaust chamber and thedownstream exhaust chamber. The partition wall includes a communicationhole that extends through the partition wall such that the upstreamexhaust chamber communicates with the downstream exhaust chamber.

According to the above aspect, the exhaust gas that has flowed into theupstream exhaust chamber flows into the downstream exhaust chamberthrough the communication hole, which extends through the partitionwall. In this case, after flowing along the outer circumferential faceof the flame stabilizer, the exhaust gas strikes the partition wall andflows along the partition wall. The exhaust gas then flows in thedepthwise direction of the partition wall (the direction in which thecommunication hole extends). For this reason, compared to when theexhaust gas flows from the upstream exhaust chamber to the downstreamexhaust chamber without changing the direction, the exhaust gas flowinginto the gap between the flame stabilizer and the cover takes a morecomplex route.

Preferably, a flow path cross-sectional area of the exhaust pipe islarger than a flow path cross-sectional area of the upstream exhaustchamber.

According to the above aspect, compared to when the flow pathcross-sectional area of the exhaust pipe is smaller than the flow pathcross-sectional area of the upstream exhaust chamber, expansion of theexhaust gas in the upstream exhaust chamber is suppressed. For thisreason, the decrease in the temperature of the exhaust gas is reduced,and therefore, the efficiency of heat transfer from the exhaust gas tothe flame stabilizer is increased.

Preferably, the burner for an exhaust purification device furthercomprises an ignition portion, which is arranged in the space in theflame stabilizer to ignite the air-fuel mixture. With respect todistances in the axial direction of the flame stabilizer, the distancebetween the partition portion and the ejection port is shorter than thedistance between the ignition portion and the ejection port. Accordingto the above aspect, with respect to distances in the axial direction ofthe flame stabilizer, compared to when the distance between thepartition portion and the ejection port is long, the flame stabilizerhas a larger outer circumferential face that defines the upstreamexhaust chamber. This facilitates increasing the temperature of theflame stabilizer with the exhaust gas flowing in the upstream exhaustchamber. With this, the temperature of gas in the combustion area ismore easily raised by being heated by the flame stabilizer. As a result,the ambient temperature is more easily raised near the ignition portionin the combustion area.

According to another aspect of the present disclosure, the burnerfurther comprises a premixing portion, which is arranged in the space inthe flame stabilizer and produces the air-fuel mixture, and an ignitionportion, which is arranged in the space in the flame stabilizer andignites the air-fuel mixture produced in the premixing portion. Thedistance between the ignition portion and the upstream exhaust chamberis shorter than the distance between the ignition portion and thedownstream exhaust chamber.

According to the above aspect, the air-fuel mixture combusted in thecombustion area is air-fuel mixture that is mixed in advance in thepremixing portion. For this reason, compared to when air-fuel mixture isproduced and combusted in the combustion area, the air-fuel mixture ismore easily ignited, and the air-fuel mixture is efficiently combusted.Furthermore, since the temperature of the gas is raised near theignition portion, the exhaust gas is efficiently utilized as heat forreducing production of unburned gas compared to when the temperature ofthe gas is raised at a distance from the ignition portion. As a result,it is possible to further suppress the discharge of fuel supplied to thecombustion area as unburned gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exhaust purification device including aburner for an exhaust purification device according to a firstembodiment;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a graph that shows a relationship between elapsed time fromcold start of an engine and an ambient temperature near an ignitionpoint in a combustion area;

FIG. 4 is a schematic view of a burner for an exhaust purificationdevice according to a second embodiment;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4; and

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 4.

MODES FOR CARRYING OUT THE INVENTION First Embodiment

A burner for an exhaust purification device according to a firstembodiment of the present disclosure will now be described withreference to FIGS. 1 to 3. First, the general configuration of anexhaust purification device including the burner for an exhaustpurification device will be described with reference to FIG. 1.

As shown in FIG. 1, an exhaust purification device 10 for a dieselengine is arranged downstream of an exhaust pipe 11, through whichexhaust gas from the engine flows. The exhaust purification device 10includes a tubular upstream cover 13 and a tubular downstream cover 14,which are coupled to each other. The downstream cover 14 includes adiesel particulate filter 12 (hereinafter, referred to as a DPF 12), towhich particulate matter contained in the exhaust gas adsorbs.

The DPF 12 has a honeycomb structure made of, e.g., a porous siliconcarbide and captures particulate matter in the exhaust gas with thesurface of the inner wall that defines the honeycomb structure. A burnerfor an exhaust purification device 15 (hereinafter, referred to as aburner 15) is mounted upstream of the DPF 12, and carries out aregeneration process of the DPF 12 by raising the temperature of theexhaust gas flowing into the DPF 12.

The upstream cover 13 is one of the components included in the burner15, and its circumference wall has a basal end fixed to a basal wall 17of the flame stabilizer 16. The upstream cover 13 is connected to anexhaust pipe 11, through which the exhaust gas from the engine flows.

The flame stabilizer 16 of the burner 15 has a tubular shape with thebasal wall 17, and its circumference wall is surrounded by the upstreamcover 13. The flame stabilizer 16 includes a small diameter portion 18and a large diameter portion 19. The small diameter portion 18 has asmaller diameter than the diameter of the basal wall 17 and is fixed tothe basal wall 17. The large diameter portion 19 extends from the distalend of the small diameter portion 18 to an ejection port 16A of theflame stabilizer 16 while increasing its diameter. The flame stabilizer16 includes a combustion area 20 formed in a space surrounded by thecircumference wall of the small diameter portion 18 and thecircumference wall of the large diameter portion 19.

An air supply pipe 26 is fixed to the basal wall 17 of the flamestabilizer 16 and guides a portion of intake air that flows through anintake pipe 25 in a state of being compressed by a compressor of aturbocharger as air for combustion to the combustion area 20. An airvalve 27 is attached to a portion of an air supply pipe 26. A portion ofthe intake air flows into the combustion area 20 through the air supplypipe 26 when the air valve 27 is in the open state.

A fuel injection valve 21 is fixed to the basal wall 17 of the flamestabilizer 16 inside a part where the circumference wall of the smalldiameter portion 18 is fixed to the basal wall 17. The fuel injectionvalve 21 is supplied with fuel by a fuel pump for supplying fuel to theengine (not shown). A distal end portion of the fuel injection valve 21,which includes an injection port, is arranged in the combustion area 20.The fuel injection valve 21 injects the fuel into the combustion area 20to supply atomized fuel to the combustion area 20.

A pair of spark plugs 22 is fixed to the basal wall 17 of the flamestabilizer 16 inside a part where the circumference wall of the smalldiameter portion 18 is fixed to the basal wall 17. The spark plugs 22are arranged such that ignition portions 22 a, which are distal endportions of the spark plugs 22, surround the distal end portion of thefuel injection valve 21. The spark plugs 22 generate sparks in thecombustion area 20 to ignite air-fuel mixture of fuel and air forcombustion at an ignition point 23. This produces flame F in thecombustion area 20.

A annular partition wall 33 is fixed to the upstream cover 13 and thesmall diameter portion 18. The partition wall 33 is a partition portionthat partitions a gap formed between the inner circumferential face ofthe upstream cover 13 and the outer circumferential face of the flamestabilizer 16 into an upstream exhaust chamber 31 and a downstreamexhaust chamber 32. The upstream exhaust chamber 31 is located close tothe basal wall 17 (basal end) of the flame stabilizer 16. The downstreamexhaust chamber 32 is located close to the ejection port 16A (distalend) of the flame stabilizer 16. In detail, the partition wall 33projects from the outer circumferential face of the small diameterportion 18 of the flame stabilizer 16 toward the inner circumferentialface of the upstream cover 13, and the partition wall 33 is coupled tothe inner circumferential face of the upstream cover 13 and the outercircumferential face of the small diameter portion 18. The partitionwall 33 is located closer to the distal end of the flame stabilizer 16(ejection port 16A) than the ignition portions 22 a in the axialdirection of the flame stabilizer 16. In other words, with respect todistances in the axial direction of the flame stabilizer 16, thedistance between the partition wall 33 and the ejection port 16A isshorter than the distance between the ignition portions 22 a and theejection port 16A. The upstream exhaust chamber 31 communicates with theexhaust pipe 11 through an opening 34 formed in the upstream cover 13.The downstream exhaust chamber 32 has an open end located opposite tothe partition wall 33. The partition wall 33 includes communicationholes 35 formed at predefined intervals in the circumferential directionof the partition wall 33. The communication holes 35 connect theupstream exhaust chamber 31 to the downstream exhaust chamber 32. Inother words, after the exhaust gas flowing through the exhaust pipe 11passes through the upstream exhaust chamber 31, the communication holes35, the downstream exhaust chamber 32 in order, the exhaust gas flowsinto the DPF 12. In this case, when the flame F is formed in thecombustion area 20, the temperature of exhaust gas is raised by theflame F, and then the exhaust gas flows into the DPF 12.

As shown in FIG. 2, the exhaust pipe 11 is shaped such that pipingextending in the radial direction of the upstream cover 13 is offsettoward the left of the upstream cover 13 and extends substantially inthe tangential direction of the outer surface of the upstream cover 13.For this reason, the exhaust gas flowing into the upstream exhaustchamber 31 from the exhaust pipe 11 partially flows into the downstreamexhaust chamber 32 through the communication holes 35 included in thepartition wall 33 while the exhaust gas flowing in the upstream exhaustchamber 31 forms a swirling flow that swirls around the small diameterportion 18 of the flame stabilizer 16 as illustrated by the arrows shownin FIG. 2.

The upstream exhaust chamber 31 is formed such that the swirling flow ofthe exhaust gas has a flow path area smaller than the flow path area ofthe exhaust pipe 11. In other words, in FIG. 1, a portion surrounded bythe small diameter portion 18, the partition wall 33, the upstream cover13, and the basal wall 17 is formed so as to have an area smaller thanthe flow path area of the exhaust pipe 11.

Operation of the burner 15 configured as above will now be describedwith reference to FIG. 3.

In the burner 15, the gap between the upstream cover 13 and the flamestabilizer 16 is partitioned by the partition wall 33 into the upstreamexhaust chamber 31 and the downstream exhaust chamber 32. The partitionwall 33 includes the communication holes 35, which connect the upstreamexhaust chamber 31 to the downstream exhaust chamber 32. In addition,the exhaust pipe 11 communicates with the upstream exhaust chamber 31.

According to this configuration, the exhaust gas which has flowedthrough the exhaust pipe 11 passes through the upstream exhaust chamber31, the communication holes 35, and the downstream exhaust chamber 32.After that, the exhaust gas flows into the DPF 12. For this reason,compared to when the partition wall 33 is not formed, the exhaust gasthat has flowed into the gap between the upstream cover 13 and the flamestabilizer 16 takes a more complex route to flow out of the gap, andtherefore, the possibility for the exhaust gas to contact thecircumference wall of the flame stabilizer 16 is increased. Thisfacilitates heating the flame stabilizer 16 with heat transferred fromthe exhaust gas and raising the temperature of gas in the combustionarea 20 heated with the flame stabilizer 16.

In other words, even when the engine is cold, the temperature of theflame stabilizer 16 and the temperature of the gas in the combustionarea 20 are promptly raised. Furthermore, after raising the temperaturesof the flame stabilizer 16 and the combustion area 20, it is easier tomaintain the raised temperatures. This facilitates vaporization of thefuel in the combustion area 20 when the engine is cold, thereby reducingthe fuel discharged as unburned gas after being supplied to thecombustion area 20.

In the burner 15, the exhaust pipe 11 is, as shown in FIG. 2, one pipethat is offset toward the left of the upstream cover 13 and extendssubstantially in the tangential direction of the outer circumferentialface of the upstream cover 13. For this reason, the exhaust gas flowinginto the upstream exhaust chamber 31 forms a swirling flow that swirlsaround the small diameter portion 18. According to this configuration,compared to when a plurality of exhaust gas pipes is connected to theupstream cover 13, it is easier to generate a swirling flow in theupstream exhaust chamber 31. In addition, compared to when the exhaustgas flowing into the upstream exhaust chamber 31 forms two flows dividedby the flame stabilizer 16 by striking the circumference wall of theflame stabilizer 16, it is easier for the exhaust gas to contact theentire surface of the portion of the circumference wall of the smalldiameter portion 18 that defines the upstream exhaust chamber 31. As aresult, heat is efficiently transferred from the exhaust gas to theflame stabilizer 16.

In the burner 15, the exhaust pipe 11 is attached to the upstream cover13 at a position such that a swirling flow is generated in the upstreamexhaust chamber 31. For this reason, for example, compared to when aguide plate for guiding the exhaust gas flowing into the upstreamexhaust chamber 31 is arranged in the upstream exhaust chamber 31 togenerate a swirling flow in the upstream exhaust chamber 31, a simplerconfiguration is employed to allow the exhaust gas to contact the entiresurface of the portion of the circumference wall of the small diameterportion 18 that defines the upstream exhaust chamber 31.

In the burner 15, the flow path cross-sectional area of the exhaust pipe11 is larger than the flow path cross-sectional area in the upstreamexhaust chamber 31. For this reason, compared to when the flow pathcross-sectional area of the exhaust pipe 11 is smaller than the flowpath cross-sectional area of the upstream exhaust chamber 31, the volumeof the upstream exhaust chamber 31 in the same flow path length issmaller, and therefore, expansion of the exhaust gas in the upstreamexhaust chamber 31 is suppressed. This reduces the decrease in thetemperature of the exhaust gas flowing in the upstream exhaust chamber31, thereby increasing the efficiency of heat transfer from the exhaustgas to the flame stabilizer 16.

In the burner 15, the partition wall 33 is arranged closer to the distalend of the flame stabilizer 16 than the ignition portions 22 a. For thisreason, compared to when the partition wall 33 is arranged closer to thebasal wall 17 of the flame stabilizer 16 than the ignition portions 22a, the circumference wall of the flame stabilizer 16 that defines theupstream exhaust chamber 31 is enlarged so that the circumference wallsurrounds the ignition point 23. As a result, the temperature of theflame stabilizer 16 is more easily raised with the exhaust gas flowingin the upstream exhaust chamber 31, and the ambient temperature is moreeasily raised near the ignition point 23 via the flame stabilizer 16.

FIG. 3 shows a graph that shows a relationship between elapsed time tfrom cold start of the engine and an ambient temperature T in thecombustion area. In FIG. 3, an example indicated by a solid linerepresents the aforementioned burner 15. A comparison example indicatedby a long dashed double-short dashed line represents a burner for anexhaust purification device in which the partition wall 33 is not formedand the exhaust pipe 11 is connected to the upstream cover 13 so as toface the large diameter portion 19. The ambient temperature T is atemperature near the ignition point 23, and an ignitable temperature T1is a temperature at which mixture of fuel and air can be ignited.

As shown in FIG. 3, in the burner 15 of the example, the ambienttemperature T near the ignition point 23 reaches the ignitabletemperature T1 in elapsed time t1. In the burner for an exhaustpurification device of the comparison example, the ambient temperature Tnear the ignition point 23 reaches the ignitable temperature T1 inelapsed time t2, which is longer than the elapsed time t1. Thus, it isrecognized that the burner 15 of the example has the ambient temperatureT near the ignition point 23 to reach the ignitable temperature T1earlier than the burner of the comparison example.

As described above, the burner 15 according to the first embodimentprovides the following advantages.

(1) Even in cold, the temperature of the flame stabilizer 16 and thetemperature of gas in the combustion area 20 heated by the flamestabilizer 16 are promptly raised. In addition, after the temperature ofthe flame stabilizer 16 is raised, it is easier to maintain the raisedtemperatures of the flame stabilizer 16 and the gas in the combustionarea 20. This reduces fuel discharged as unburned gas after beingsupplied to the combustion area 20.

(2) Since the swirling flow that swirls around the flame stabilizer 16is generated in the upstream exhaust chamber 31, it is easier for theexhaust gas to contact the entire surface of the portion of thecircumference wall of the flame stabilizer 16 that defines the upstreamexhaust chamber 31, and heat is efficiently transferred from the exhaustgas to the flame stabilizer 16.

(3) The exhaust pipe 11 is attached to the upstream cover 13 at theposition such that a swirling flow is generated in the upstream exhaustchamber 31. Thus, compared to when a member such as a guide plate isarranged in the upstream exhaust chamber 31, a simpler configuration canbe employed to allow the exhaust gas to contact the entire surface ofthe portion of the circumference wall of the flame stabilizer 16 thatdefines the upstream exhaust chamber 31.

(4) The exhaust gas flowing into the upstream exhaust chamber 31 flowsalong the partition wall 33, and then flows into the downstream exhaustchamber 32 through the communication holes 35 of the partition wall 33.In this case, in order to flow from the upstream exhaust chamber 31 tothe downstream exhaust chamber 32, the exhaust gas needs to change theflowing direction so as to flow in the depthwise direction of thepartition wall 33 after flowing along the face of the partition wall 33.For this reason, compared to when the exhaust gas flows from theupstream exhaust chamber 31 to the downstream exhaust chamber 32 withoutchanging the flowing direction of the exhaust gas, the exhaust gas takesa more complex route, and therefore, the efficiency of heat transferfrom the exhaust gas to the flame stabilizer 16 is increased.

(5) The flow path cross-sectional area of the exhaust pipe 11 is largerthan the flow path cross-sectional area of the upstream exhaust chamber31. Thus, compared to when the flow path cross-sectional area of theexhaust pipe 11 is smaller than the flow path cross-sectional area ofthe upstream exhaust chamber 31, the volume in the upstream exhaustchamber 31 per the same flow path length is smaller than the volume inthe exhaust pipe 11, and therefore, expansion of exhaust gas in theupstream exhaust chamber 31 is suppressed. Accordingly, heat isefficiently transferred from the exhaust gas to the flame stabilizer 16.

(6) The partition wall 33 is arranged closer to the ejection port 16A ofthe flame stabilizer 16 than the ignition portions 22 a. Thus, comparedto when the partition wall 33 is arranged closer to the basal wall 17 ofthe flame stabilizer 16 than the ignition portions 22 a, it is easier toraise the temperature of the flame stabilizer 16. As a result, thetemperature of gas in the combustion area 20 is more easily raised bybeing heated by the flame stabilizer 16.

Second Embodiment

A burner for an exhaust purification device according to a secondembodiment of the present disclosure will now be described withreference to FIGS. 4 to 6. The burner for an exhaust purification device50 according to the second embodiment is primarily configured in thesame way as the burner for an exhaust purification device according tothe first embodiment. For this reason, in the second embodiment, partsdifferent from the first embodiment will be described in detail, andparts with similar functions to those in the first embodiment will notbe described in detail by assigning like reference characters.

As shown in FIG. 4, in the burner for an exhaust purification device 50(hereinafter, simply referred to as a burner 50), the flame stabilizer16 has a cylindrical tube shape that has a bottom and is opened towardthe DPF 12. The basal wall 17 in the flame stabilizer 16 closes theopening at the basal end of the small diameter portion 18 in the flamestabilizer 16 and extends radially outward from the portion fixed to thesmall diameter portion 18.

A tubular outer tube 51 is fixed to the edge of the basal wall 17 of theflame stabilizer 16. The outer tube 51 extends from the edge of thebasal wall 17 toward the DPF 12, and surrounds the entire small diameterportion 18 of the flame stabilizer 16. The distal end portion of theouter tube 51, which is the one of two ends that is located close to theDPF 12, is fixed to an annular closing wall 53. The distal end portionof the outer tube 51 is arranged closer to the basal wall 17 than theejection port 16A of the flame stabilizer 16. An area between the outercircumferential face of the small diameter portion 18 and the innercircumferential face of the outer tube 51 is sandwiched and closed bythe basal wall 17 and the closing wall 53.

The closing wall 53 has an outer circumferential edge fixed to thetubular upstream cover 13. The upstream cover 13 extends from the outercircumferential edge of the closing wall 53 toward the DPF 12 andsurrounds the entire large diameter portion 19 of the flame stabilizer16. The gap between the outer circumferential face of the large diameterportion 19 and the inner circumferential face of the upstream cover 13is opened toward the DPF 12. The upstream cover 13 serves as a tubularcover that surrounds the flame stabilizer 16.

The partition wall 33 is arranged in the gap between the outercircumferential face of the large diameter portion 19 and the innercircumferential face of the upstream cover 13. The annular partitionwall 33 resides along a periphery of the large diameter portion 19. Thepartition wall 33 partitions the gap between the outer circumferentialface of the large diameter portion 19 and the inner circumferential faceof the upstream cover 13 in the axial direction of the flame stabilizer16 into the upstream exhaust chamber 31 and the downstream exhaustchamber 32. The upstream exhaust chamber 31 is a space connected to theexhaust pipe 11, and the downstream exhaust chamber 32 is a spaceconnected to the ejection port 16A. The partition wall 33 has thecommunication holes 35, which extend through the partition wall 33 toconnect the upstream exhaust chamber 31 to the downstream exhaustchamber 32.

As shown in FIG. 5, the outer circumferential face of the outer tube 51is connected to the air supply pipe 26, and a guide plate 54 is arrangedon the inner circumferential face of the outer tube 51 near the outletof the air supply pipe 26. The guide plate 54 is positioned to beseparated from the outlet of the air supply pipe 26 and to face theoutlet. The area between the outer circumferential face of the smalldiameter portion 18 and the outer tube 51 is an introduction flow path52. The air for combustion that enters the introduction flow path 52from the air supply pipe 26 is guided by the guide plate 54, and turnsalong the outer circumferential face of the small diameter portion 18.

The small diameter portion 18 has an end (basal end) fixed to the basalwall 17 and has a plurality of first introduction ports 55 extendingthrough the small diameter portion 18 in a portion located near thebasal end. The first introduction ports 55 line up at equal intervals inthe circumferential direction of the small diameter portion 18. Thespace surrounded by the flame stabilizer 16 is the combustion area 20,and the first introduction ports 55 lead a portion of the air forcombustion that has entered the introduction flow path 52 to the insideof the flame stabilizer 16.

The portion of the small diameter portion 18 that is located closer tothe ejection port 16A than the first introduction ports 55 includes aplurality of second introduction ports 56, which extends through thesmall diameter portion 18. The second introduction ports 56 line up atequal intervals in the circumferential direction of the flame stabilizer16. The second introduction ports 56 lead the air for combustion thathas entered the introduction flow path 52 to the inside of the flamestabilizer 16.

As shown in FIG. 6, a raised piece 57 is formed at the opening edge ofeach first introduction port 55 by cutting a portion of thecircumference wall of the small diameter portion 18 and raising theportion inward. The raised piece 57 guides air for combustion from thefirst introduction port 55 to the inside of the flame stabilizer 16, andswirls the air for combustion inside the flame stabilizer 16. The raisedpiece 57 swirls the air for combustion in the swirling direction of theair for combustion in the introduction flow path 52 inside the flamestabilizer 16.

A fuel supply unit 58, which supplies fuel to the inside of the flamestabilizer 16, is fixed to the basal wall 17. The distal end portion ofthe fuel supply unit 58, which includes a supply port, is arrangedinside the flame stabilizer 16. The fuel supply unit 58 is connected toa fuel pump for supplying fuel to the engine through a fuel valve. Fuelis sent to the fuel supply unit 58 by the fuel pump when the fuel valveis opened. The fuel sent to the fuel supply unit 58 is vaporized in thefuel supply unit 58 and injected to the inside of the flame stabilizer16.

A coupling portion 60 is coupled to the portion of the innercircumferential face 16 b of the small diameter portion 18 that residesbetween the first introduction ports 55 and the second introductionports 56 in the flame stabilizer 16. The coupling portion 60 includes aflange 61, an insertion portion 62, and a radially-narrowed portion 63.The flange 61, the insertion portion 62, and the radially-narrowedportion 63 are integrated.

The flange 61 is annular and resides along the inner circumferentialface 16 b of the small diameter portion 18 and fixed to the entire innercircumferential face 16 b of the small diameter portion 18 in thecircumferential direction of the inner circumferential face 16 b. In thespace surrounded by the flame stabilizer 16, the flange 61 and the basalwall 17 define a first mixing chamber 71.

Air for combustion enters the first mixing chamber 71 through the firstintroduction ports 55, and fuel enters the first mixing chamber 71 fromthe fuel supply unit 58. The air for combustion swirls around the axisof the flame stabilizer 16 and the fuel is injected toward the center ofthe swirling air for combustion so that the air for combustion and thefuel are mixed in the first mixing chamber 71.

The insertion portion 62 has a tubular shape extending from theradially-narrowed portion 63 toward the ejection port 16A and has asmaller diameter than the inner diameter of the flange 61. Theradially-narrowed portion 63 has a tubular truncated cone shapeextending from the inner circumferential edge of the flange 61 towardthe ejection port 16A and couples the flange 61 with the insertionportion 62.

A tubular first inner tube 64 is inserted into the insertion portion 62.The basal end of the first inner tube 64, which is the one of two endsthat is located close to the basal wall 17, is joined to the insertionportion 62. The flange 61 of the coupling portion 60 is coupled to theinner circumferential face 16 b of the flame stabilizer 16, and theinsertion portion 62 of the coupling portion 60 is coupled to the outercircumferential face 64 a of the first inner tube 64. The couplingportion 60 closes an area between the inner circumferential face 16 b ofthe flame stabilizer 16 and the outer circumferential face 64 a of thefirst inner tube 64. The distal end of the first inner tube 64, which isthe one of two ends that is located close to the ejection port 16A, isopened.

A tubular second inner tube 65 is arranged around the first inner tube64 to surround the first inner tube 64. The distal end portion of thefirst inner tube 64 is surrounded by the second inner tube 65. The end(distal end) of the second inner tube 65 that is located close to theejection port 16A is positioned closer to the ejection port 16A than thedistal end of the first inner tube 64. The end (basal end) of the secondinner tube 65 that is located close to the basal wall 17 is positionedcloser to the ejection port 16A than the basal end of the first innertube 64.

The opening at the distal end of the second inner tube 65 is closed by aclosing wall 66. The basal end of the second inner tube 65 is fixed tothe inner circumferential face of the small diameter portion 18 with anannular support plate 67.

The inner circumferential edge of the support plate 67 is fixed to theentire outer circumferential face 65 a of the second inner tube 65. Theouter circumferential edge of the support plate 67 is fixed to theentire inner circumferential face 16 b of the flame stabilizer 16. Aplurality of communication passages 68 extends through the support plate67 so that the space located closer to the ejection port 16A than thesupport plate 67 communicates with the space located closer to the basalwall 17 than the support plate 67. A wire mesh 69, which covers thecommunication passages 68, is attached to the support plate 67.

The space surrounded by the inner circumferential face of the firstinner tube 64 in the space surrounded by the flame stabilizer 16 forms asecond mixing chamber 72. The air-fuel mixture coming out of the firstmixing chamber 71 enters the second mixing chamber 72.

In the space surrounded by the flame stabilizer 16, the space that islocated closer to the ejection port 16A than the second mixing chamber72 and surrounded by the inner circumferential face of the second innertube 65 and the closing wall 66 forms a third mixing chamber 73. Theair-fuel mixture coming out of the second mixing chamber 72 enters thethird mixing chamber 73.

In the space surrounded by the flame stabilizer 16, the area between theouter circumferential face of the first inner tube 64 and the innercircumferential face of the second inner tube 65 forms a fourth mixingchamber 74. The air-fuel mixture coming out of the third mixing chamber73 enters the fourth mixing chamber 74.

In the space surrounded by the flame stabilizer 16, the area surroundedby the inner circumferential face 16 b of the flame stabilizer 16, thesupport plate 67, and the coupling portion 60 forms a fifth mixingchamber 75. The air-fuel mixture coming out of the fourth mixing chamber74 enters the fifth mixing chamber 75.

The spark plug 22 is fixed to the outer circumferential face of theouter tube 51. The ignition portion 22 a of the spark plug 22 projectsinward of the flame stabilizer 16 from the inner circumferential face 16b of the flame stabilizer 16. The ignition portion 22 a is arranged inthe space between the inner circumferential face of the small diameterportion 18 and the outer circumferential face 65 a of the second innertube 65 and positioned closer to the ejection port 16A than the supportplate 67 in the axial direction of the flame stabilizer 16. The distancebetween the ignition portion 22 a and the upstream exhaust chamber 31 inthe axial direction of the flame stabilizer 16 is shorter than thedistance between the ignition portions 22 a and the downstream exhaustchamber 32.

The first mixing chamber 71, the second mixing chamber 72, the thirdmixing chamber 73, the fourth mixing chamber 74, and the fifth mixingchamber 75 form one premixing chamber 70, which serves as a premixingportion for producing air-fuel mixture. The space between the innercircumferential face 16 b of the flame stabilizer 16 and the outercircumferential face 65 a of the second inner tube 65 and the spacelocated closer to the ejection port 16A than the closing wall 66 in theflame stabilizer 16 form the combustion area 20. The premixing chamber70 and the combustion area 20 are comparted with a compartment portionincluding the second inner tube 65, the closing wall 66, and the supportplate 67. The air-fuel mixture produced in the premixing chamber 70enters the combustion area 20 through the communication passages 68 andis then ignited by the ignition portion 22 a.

As described above, the burner 50 according to the second embodimentprovides the following advantages in addition to the above advantages(1) to (5).

(7) Before entering the combustion area 20 to be combusted, fuel ismixed with air for combustion in advance in the premixing chamber 70.For this reason, compared to the configuration in which air-fuel mixtureis not produced in the premixing chamber 70, it is easier to ignite theair-fuel mixture, and the air-fuel mixture is efficiently combusted. Asa result, it is possible to further suppress the discharge of fuelsupplied to the combustion area as unburned gas.

(8) The distance (shortest distance) between the ignition portions 22 aand the upstream exhaust chamber 31 is shorter than the distance(shortest distance) between the ignition portion 22 a and the downstreamexhaust chamber 32. Further, the temperature of the exhaust gas flowingin the upstream exhaust chamber 31 is transferred via the flamestabilizer 16. This raises the temperature of gas near the ignitionportion 22 a. Thus, compared to the configuration in which thetemperature of gas is raised at a distance from the ignition portions 22a, the exhaust gas is efficiently utilized as heat for reducingproduction of unburned gas.

(9) Before entering the first mixing chamber 71, the air for combustionflowing in the introduction flow path 52 contacts the outercircumferential face of the flame stabilizer 16 and is heated with theouter circumferential face. As a result, it is easier to ignite theair-fuel mixture, and the air-fuel mixture is efficiently combusted.

(10) The outer circumferential face of the large diameter portion 19defines the upstream exhaust chamber 31. Thus, compared to theconfiguration in which the outer circumferential face of the smalldiameter portion 18 defines the upstream exhaust chamber 31, the contactarea of the outer circumferential face of the flame stabilizer 16 withthe exhaust gas is enlarged.

The first and second embodiments may be modified in the following forms.

In the first embodiment, the partition wall 33 may be arranged closer tothe basal wall 17 of the flame stabilizer 16 than the ignition portions22 a. In other words, with respect to distances in the axial directionof the flame stabilizer 16, the distance between the partition wall 33and the ejection port 16A may be longer than the distance between theignition portions 22 a and the ejection port.

In the second embodiment, the second introduction ports 56 may beomitted. In other words, air for combustion may be supplied to thecombustion area 20 only through the premixing chamber 70.

In the second embodiment, the air supply pipe 26 may be connected to thebasal wall 17. In other words, air for combustion may enter thepremixing chamber 70 without traveling around the flame stabilizer 16.

In the second embodiment, the compartment portion, which comparts thepremixing chamber 70 and the combustion area 20, may be, e.g., a flatplate arranged inside the flame stabilizer 16 to be orthogonal to theaxial direction of the stabilizer 16. In other words, the compartmentportion, which comparts the premixing chamber 70 and the combustion area20, may be modified as long as it is configured as a member thatpartitions a space defined by the flame stabilizer 16 into a spaceproducing air-fuel mixture and a space for igniting the air-fuel mixture(combustion area).

In the configuration in which the compartment portion includes thecoupling portion 60, the first inner tube 64, the second inner tube 65,the closing wall 66, and the support plate 67, a passage that connectsthe space for producing air-fuel mixture and the space for igniting theair-fuel mixture (combustion area) is complicated. For this reason, inview of mixing fuel and air for combustion to a great extent, it ispreferable for the compartment portion to include the coupling portion60, the first inner tube 64, the second inner tube 65, the closing wall66, and the support plate 67.

The distance between the ignition portion 22 a and the upstream exhaustchamber 31 may be equal to the distance between the ignition portion 22a and the downstream exhaust chamber 32, or may be longer than thedistance between the ignition portion 22 a and the downstream exhaustchamber 32.

For example, in the axial direction of the flame stabilizer 16, theignition portion 22 a may be arranged midway between the upstreamexhaust chamber 31 and the downstream exhaust chamber 32. In this case,the upstream exhaust chamber 31 and the downstream exhaust chamber 32may be partitioned by two or more partition walls. In the configurationthat partitions with one partition wall, the ignition portion 22 a maybe arranged inside the flame stabilizer 16 through the partition wall.With this configuration, the distance between the ignition portion 22 aand the upstream exhaust chamber 31 is set to be equal to the distancebetween the ignition portion 22 a and the downstream exhaust chamber 32or to be longer than the distance between the ignition portion 22 a andthe downstream exhaust chamber 32.

For example, the upstream exhaust chamber 31 may be defined by apartition wall and another wall different from the partition wall andarranged closer to the ejection port 16A than the downstream exhaustchamber 32. In this case, piping that connects the downstream exhaustchamber 32 and the ejection port 16A may be modified as long as it isconfigured to be separately provided outside of the cover so that theexhaust gas of the downstream exhaust chamber 32 travels outside thecover and flows to the ejection port 16A.

For example, the partition wall may extend in the direction that crossesthe circumferential direction of the flame stabilizer 16, and partitionthe upstream exhaust chamber 31 off from the downstream exhaust chamber32 in the direction that crosses the circumferential direction of theflame stabilizer 16. With this configuration, in the radial direction ofthe flame stabilizer 16, the upstream exhaust chamber 31 and thedownstream exhaust chamber 32 are arranged outside of the ignitionportion 22 a. For this reason, the distance between the ignition portion22 a and the upstream exhaust chamber 31 is equal to the distancebetween the ignition portion 22 a and the downstream exhaust chamber 32,or longer than the distance between the ignition portion 22 a and thedownstream exhaust chamber 32.

In other words, the partition portion may be modified as long as it isconfigured to partition the gap between the outer circumferential faceof the flame stabilizer and the inner circumferential face of the coverinto the upstream exhaust chamber 31 connected to the exhaust pipe andthe downstream exhaust chamber 32 connected to the ejection port.

The flow path cross-sectional area of the exhaust pipe 11 may be lessthan or equal to the flow path cross-sectional area of the upstreamexhaust chamber 31.

The configuration for generating a swirling flow in the upstream exhaustchamber 31 is not limited to the exhaust pipe 11 that is offset from theupstream cover 13, but may be formed, e.g., by arranging a guide platefor guiding the exhaust gas flowing into the upstream exhaust chamber 31in the upstream exhaust chamber 31. According to the first and secondembodiments, the upstream exhaust chamber 31 is a continuous annularspace. However, another configuration for generating a swirling flow inthe upstream exhaust chamber 31 may be employed, e.g., by forming theupstream exhaust chamber 31 with a discontinuous space by a stopperarranged near the portion that connects the upstream cover 13 and theexhaust pipe 11.

In the upstream exhaust chamber 31, for example, the exhaust pipe 11 mayextend in the radial direction of the outer surface of the upstreamcover 13 so that the exhaust gas flowing from the exhaust pipe 11 isdivided by the flame stabilizer 16 to form two flows. In addition, aplurality of exhaust pipes 11 may be connected to the upstream exhaustchamber 31 so that the exhaust gas flowing from the exhaust pipes 11flows in different directions. In other words, this may be modified aslong as it is configured that the exhaust gas of the exhaust pipes 11passes through the upstream exhaust chamber 31, the communication holes35, and the downstream exhaust chamber 32 in order.

The communication holes 35 may be omitted, and the partition portion maybe configured such that the partition wall 33 is separated from theinner surface of the upstream cover 13. The communication holes 35 maybe omitted, and the partition portion may be configured such that thepartition wall 33 is separated from the circumference wall of the flamestabilizer 16. The partition portion may be configured to include two ormore partition walls 33 configured as above. The plurality ofcommunication holes 35 may be omitted from the partition wall 33, andthe upstream exhaust chamber 31 and the downstream exhaust chamber 32,which are partitioned by the partition wall 33, may be connected by,e.g., other piping arranged outside of the upstream cover 13.

Not limited to piping for exhaust gas from the engine, the exhaust pipe11 may be piping through which the exhaust gas that has passed throughthe DPF 12 flows.

The flame stabilizer 16 may have a tubular shape that has a constantdiameter over the entire flame stabilizer in the axial direction. Inother words, the flame stabilizer 16 may be modified as long as it isconfigured to have a tubular shape with the ejection port 16A forejecting combustion gas.

The fuel injected from the fuel injection valve 21 may be supplied froma common rail, not a fuel pump. A fuel pump that supplies fuel only tothe fuel injection valve 21 may be included.

In the first embodiment, for example, the fuel injection valve 21 may beconfigured to supply fuel that is vaporized in advance to the combustionarea 20.

In the second embodiment, the fuel supply unit 58 may inject fuel thatis not vaporized to the first mixing chamber 71.

Not limited to a spark plug, a glow plug, a laser spark device, or aplasma spark device may be used to ignite air-fuel mixture. One of thoseor two or more of those may be used to ignite the air-fuel mixture.

Not limited to the intake air flowing through the intake pipe 25, airfor combustion may be air flowing through piping connected to the airtank of a brake or air supplied by a blower for the burner for anexhaust purification device.

The engine with the burner for an exhaust purification device may be agasoline engine.

The exhaust gas with the temperature raised by the burner for an exhaustpurification device is used for raising the temperature of a catalyst,not limited to a regeneration process of the DPF 12.

DESCRIPTION OF THE REFERENCE NUMERALS

-   -   F: flame, T: ambient temperature, T1: ignitable temperature, t,        t1, t2: elapsed time, 10: exhaust purification device, 11:        exhaust pipe, 12: diesel particulate filter, 13: upstream cover,        14: downstream cover, 15: burner for an exhaust purification        device, 16: flame stabilizer, 16A: ejection port, 17: basal        wall, 18: small diameter portion, 19: large diameter portion,        20: combustion area, 21: fuel injection valve, 22: spark plug,        22 a: ignition portion, 23: ignition point, 25: intake pipe, 26:        air supply pipe, 27: air valve, 31: upstream exhaust chamber,        32: downstream exhaust chamber, 33: partition wall, 34: opening,        35: communication hole, 50: burner for an exhaust purification        device, 51: outer tube, 52: introduction flow path, 53: closing        wall, 54: guide plate, 55: first introduction port, 56: second        introduction port, 57: raised piece, 58: fuel supply unit, 60:        coupling portion, 61: flange, 62: insertion portion, 63:        radially-narrowed portion, 64: first inner tube, 65: second        inner tube, 66: closing wall, 67: support plate, 68:        communication passage, 69: wire mesh, 70: premixing chamber, 71:        first mixing chamber, 72: second mixing chamber, 73: third        mixing chamber, 74: fourth mixing chamber, and 75: fifth mixing        chamber.

1. A burner for an exhaust purification device, comprising: a tubularflame stabilizer having a space including a combustion area, in whichair-fuel mixture of fuel and air is combusted, an ejection port forejecting combustion gas, a small diameter portion, and a large diameterportion having an inner diameter larger than the small diameter portion;a tubular cover that surrounds the flame stabilizer, wherein a gap isformed between an inner circumference face of the cover and an outercircumference face of the flame stabilizer; an exhaust pipe connected tothe cover to deliver exhaust gas into the gap; and a partition portionarranged in the gap to partition the gap into an upstream exhaustchamber and a downstream exhaust chamber, wherein the partition portionis arranged between an outer circumference face of the large diameterportion and the inner circumference face of the cover in the gap,wherein the upstream exhaust chamber is connected to the exhaust pipeand the downstream exhaust chamber, and the downstream exhaust chamberis connected to the ejection port of the flame stabilizer.
 2. The burnerfor an exhaust purification device according to claim 1, wherein theflame stabilizer is shaped as a cylindrical tube, and the exhaust pipeextends in the tangential direction of the outer circumferential face ofthe flame stabilizer.
 3. The burner for an exhaust purification deviceaccording to claim 2, wherein the exhaust pipe connects to an outercircumferential face of the cover at one location.
 4. The burner for anexhaust purification device according to claim 1, wherein the partitionportion is configured to: protrude from the outer circumferential faceof the flame stabilizer toward the inner circumferential face of thecover; be coupled to the outer circumferential face of the flamestabilizer and the inner circumferential face of the cover; and be apartition wall that partitions the gap into the upstream exhaust chamberand the downstream exhaust chamber, and the partition wall includes acommunication hole that extends through the partition wall such that theupstream exhaust chamber communicates with the downstream exhaustchamber.
 5. The burner for an exhaust purification device according toclaim 1, wherein a flow path cross-sectional area of the exhaust pipe islarger than a flow path cross-sectional area of the upstream exhaustchamber.
 6. The burner for an exhaust purification device according toclaim 1, further comprising an ignition portion, which is arranged inthe space in the flame stabilizer to ignite the air-fuel mixture,wherein with respect to distances in the axial direction of the flamestabilizer, a distance between the partition portion and the ejectionport is shorter than a distance between the ignition portion and theejection port.
 7. The burner for an exhaust purification deviceaccording to claim 1, further comprising: a premixing portion, which isarranged in the space in the flame stabilizer and produces the air-fuelmixture; and an ignition portion, which is arranged in the space in theflame stabilizer and ignites the air-fuel mixture produced in thepremixing portion, wherein a distance between the ignition portion andthe upstream exhaust chamber is shorter than a distance between theignition portion and the downstream exhaust chamber.